Now plenty of extensions do install successfully.Why those two particular extensions don't, can't say?Is it the particular contents of those two ("hack") files, don't know?Expected behavior, or a bug, don't know?

When using the by-pass hack, if you run into difficulty installing an add-on and get this corrupt warning:

You will need to temporarily remove the config-prefs.js or autoconfig.js files to be able to install some add-ons (remove them with FX closed). Once the add-on is installed, put the file back to continue using the add-ons.